Colorado landscapers uncover a weapons cache in a planned koi pond, and they phone a nearby archaeologist instead of police. Good call: The blood-spattered tools were abandoned 13,000 years ago.

Landscapers excavating for a koi pond in Boulder, Colo., found a cache of blood-spattered weapons and tools, but instead of calling the police, they summoned an archaeologist from the University of Colorado, six blocks from the site.

Douglas B. Bamforth initially thought the stone implements might have been a few hundred years old, but further studies showed that they were left behind about 13,000 years ago, making them one of only two caches of tools from that period known to exist, the university announced Wednesday. The other cache was found in Washington state.

An analysis by anthropologist Robert Yohe of Cal State Bakersfield showed that the blood came from horses, sheep, bears and a now-extinct camel -- the first time a camel's blood has been found on such a tool.

Workers building the pond for Pharmion Corp. founder Patrick Mahaffy discovered 83 items packed into an area about the size of a shoe box.

The find was made in May, but was not announced until the blood was analyzed.

The tools are known as the Mahaffy cache. The biotech mogul -- whose firm was acquired in 2007 by Celgene Corp. -- paid for the analysis.

Among the flint implements were a salad-plate-size bifacial knife; a tool resembling a double-bitted ax; small blades; and flint scrapers.

Bamforth initially suspected that the tools were ceremonial, but the blood indicates that they were used for more practical purposes.

"It looks like someone gathered together some of their most spectacular tools and other scraps of potentially useful material and stuck them into a small hole in the ground by a stream, fully expecting to come back at a later date and retrieve them," Bamforth said.